In an internal combustion engine for a vehicle or the like, when a ring gear is provided for transmitting torque from a starter motor to a crankshaft, that ring gear is usually formed on an outer peripheral portion of a flywheel. Also, when a torque converter is provided, the ring gear may be formed on an outer peripheral portion of a drive plate which is fixed to a cover of the torque converter and transmits the rotation of the crankshaft.
Japanese Patent Application Publication No. JP-A-2000-274337, for example, discloses one such startup torque transmitting mechanism of an internal combustion engine, in which a one-way clutch is interposed between a ring gear and a flywheel so that a pinion gear on the starter motor side can be in constant mesh with the ring gear. Accordingly, the torque of the ring gear when the ring gear is rotated by the starter motor is transmitted to the crankshaft via the one-way clutch and the flywheel. When the crankshaft rotates from the output of the internal combustion engine, the one-way clutch releases so that torque from the crankshaft is not transmitted to the ring gear side.
In an internal combustion engine provided with a torque converter, it is possible to connect the ring gear to a drive plate, which transmits torque from the crankshaft to a cover of the torque converter, via the one-way clutch instead of connecting the ring gear to the flywheel. If the one-way clutch can be arranged on the drive plate in this way, torque from the ring gear that is rotated by the starter motor can be transmitted to the crankshaft via the drive plate while the ring gear is in constant mesh with the starter motor side, just as when a flywheel is used.
However, when employing a structure which transmits torque from the ring gear to a flywheel or a drive plate via a one-way clutch as described above, impact noise produced at the moment the one-way clutch engages immediately after the starter motor starts to be driven is directly transmitted to the flywheel or the drive plate. Therefore, noise may result from noise radiation from the flywheel or noise radiation from the drive plate itself or from the cover of the torque converter that is connected to the drive plate.
It is thus an object of the invention to reduce noise produced during engagement of a one-way clutch in a startup torque transmitting mechanism of an internal combustion engine which employs a one-way clutch.